Melt-processible poly(tetrafluoroethylene)

ABSTRACT

Melt-processible, thermoplastic poly(tetrafluoroethylene) (PTFE) compositions are disclosed and methods for making and processing same. Additionally, products comprising these compositions are described.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. provisionalapplication 60/095,583 filed Aug. 6, 1998 the entire disclosure of whichis hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] This invention relates to melt-processiblepoly(tetrafluoroethylene) (PTFE), compositions thereof, articles formedtherefrom, and methods for making the same. More particularly, thepresent inventions relates to a particular range ofpoly(tetrafluoroethylene) polymers which are readily melt-processiblewhile maintaining good/suitable mechanical properties. Further, thepresent invention relates to products made of melt-processible,thermoplastic PTFE compositions.

BACKGROUND OF THE INVENTION

[0003] Poly(tetrafluoroethylene) (PTFE) is well-known for, among otherproperties, its chemical resistance, high temperature stability,resistance against ultra-violet radiation, low friction coefficient andlow dielectric constant. As a result, it has found numerous applicationsin harsh physico-chemical environments and other demanding conditions.Equally well-known is the intractability of this important polymer.Numerous textbooks, research articles, product brochures and patentsstate that PTFE is intractable because, above its crystalline meltingtemperature, it does not form a fluid phase that is of a viscosity thatpermits standard melt-processing techniques commonly used for mostthermoplastic polymers (Modern Fluoropolymers, J. Scheirs, Ed. Wiley(New York), 1997; The Encyclopaedia of Advanced Materials, Vol. 2,D.Bloor et al. Eds., Pergamon (Oxford) 1994; WO 94/02547; WO 97/43102).Suitability of a polymer for standard melt-processing techniques may beevaluated, for example, through measurement of the melt-flow index ofthe material (cf. ASTM D1238-88). Melt-processible polymers should,according to this widely employed method, exhibit at least a non-zerovalue of the melt-flow index, which is not the case for common PTFEunder testing conditions that are representative of, and comparable tothose encountered in standard polymer melt-processing. The extremelyhigh viscosity of PTFE, reported to be in the range of 10¹⁰-10¹³ Pa.s at380° C., is believed to be associated, among other things, with anultra-high molecular weight of the polymer, which has been estimated tobe in the regime well above 1,000,000 g/mol and often is quoted to be ofthe order of 10,000,000 g/mol. In fact, it is claimed (ModernFluoropolymers, J. Scheirs, Ed. Wiley (New York), 1997, p. 240) that “toachieve mechanical strength and toughness, the molecular weight of PTFEis required to be in the range 10⁷-10⁸ g/mol . . . ”. Due to this highviscosity, common PTFE is processed into useful shapes and objects withtechniques that are dissimilar to standard melt-processing methods.Rods, sheets, membranes, fibers and coatings of PTFE are produced by,for example, ram-extrusion, pre-forming and sintering of compressedpowder, optionally followed by machining or skiving, paste-extrusion,high isostatic pressure processing, suspension spinning, and the like,and direct plasma polymerization. Unfortunately, these methods generallyare less economical than common melt-processing, and, in addition,severely limit the types and characteristics of objects and productsthat can be manufactured with this unique polymer. For example, commonthermoplastic polymers, such as polyethylene, isotactic polypropylene,nylons, poly(methylmethacrylate) polyesters, and the like, can readilybe melt-processed into a variety forms and products that are of complexshapes, and/or exhibit, for example, some of the followingcharacteristics: dense, void-free, thin, clear or translucent; i.e.properties that are not readily, if at all, associated with productsfabricated from PTFE.

[0004] The above drawback of PTFE has been recognised virtually sinceits invention, and ever since, methods have been developed to circumventthe intractability of the polymer. For example, a variety of co-monomershave been introduced in the PTFE macromolecular chains that lead toco-polymers of reduced viscosity and melting temperature. Co-polymersare those that are polymerized with, for example, hexafluoropropylene,perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether),perfluoro(propyl vinyl ether), or perfluoro-(2,2-dimethyl-1,3-dioxole),partially-fluorinated monomers and combinations thereof, in addition tothe tetrafluoroethylene monomer. Several of the resulting co-polymers(for example, those referred to as FEP, MFA, PFA and Teflon® AF) provideimproved processibility, and can be processed with techniques for commonthermoplastic polymers (WO 98/58105). However, a penalty is paid interms of some or all of the outstanding properties of the homopolymerPTFE, such as reduced melting temperature and thermal and chemicalstability.

[0005] Additional methods to process the PTFE homopolymer include, forexample, the addition of lubricants, plasticizers, and processing aids,as well as oligomeric polyfluorinated substances and hydrocarbylterminated TFE-oligomers (for example, Vydax® 1000) (U.S. Pat. Nos.4,360,488; 4,385,026 and WO 94/02547). The latter method, however, isdirected to the improvement of the creep resistance of common PTFE whichresults in a bimodal morphology with two distinct melting temperatures,and generally does not lead to homogeneous PTFE compositions that can bemelt-processed according to standard methods. For example, only ahot-compression molding method is heretofore known for mixtures ofstandard PTFE and Vydax® 1000, that preferably is carried out in thenarrow temperature range between about 330° C. to 338° C. The otheraforementioned additions of lubricants, plasticizers, and processingaids also do not yield truly melt-processible PTFE compositions.Solution processing, at superautogeneous pressure, of PTFE fromperfluoroalkanes containing 2-20 carbon atoms has been disclosed in WO94/15998. The latter process is distinctly different frommelt-processing methods. Also disclosed is dispersion, and subsequentmelt-processing of standard PTFE into thermoplastic (host-) polymerssuch as polyetheretherketone and polyphenylene sulfide (WO 97/43102) andpolyacetal (DE 41 12 248 A1). The latter method compromises importantphysico-chemical properties of the resulting composition, when comparedto neat PTFE, or requires uneconomical and cumbersome removal of thehost material.

[0006] There exist PTFE grades of low molecular weight and of lowviscosity. These grades, which are often are referred to asmicropowders, commonly are used as additives in inks, coatings and inthermoplastic and other polymers to impair, for example, nucleation,internal lubrication or other desirable properties that, in part, stemfrom the unique physico-chemical properties of the neat PTFE. Lowmolecular weight PTFE grades, in their solid form, unfortunately,exhibit extreme brittleness and, according to at least one of thesuppliers, these PTFE grades . . . “are not to be used as molding orextrusion powders” (Du Pont, Zonyl® data sheets and url:http://www.dupont.con/teflon/fluoroadditives/about.html—Jul. 7, 1998).

[0007] Thus, a need continues to exist to develop melt-processible,thermoplastic poly(tetrafluoroethylene)s to exploit the outstandingproperties of this polymer in a wider spectrum of product forms, as wellas to enable more economical processing of this unique material.

SUMMARY OF THE INVENTION

[0008] Surprisingly, it has been found that poly(tetrafluoroethylene)sof a particular set of physical characteristics provide a solution tothe above, unsatisfactory situation.

[0009] Accordingly, it is one objective of the present invention toprovide melt-processible, thermoplastic PTFE compositions of goodmechanical properties comprising PTFE grades that are characterized ashaving a non-zero melt-flow index in a particular range. As usedhereinafter, the indication “good mechanical properties” means thepolymer has properties suitable for use in thermoplastic applications,preferably including applications such as melt-processed thermoplasticformed into unoriented, solid fibers or films exhibiting an elongationat break of at least 10%, determined under standard ambient conditionsat a rate of elongation of 100% per min.

[0010] Yet another object of the present invention is to providemelt-processible PTFE of good mechanical properties that exhibit aplateau value of the complex viscosity measured at frequencies belowabout 0.01 rad/s and at a temperature of 380° C. that is in a rangebeneficial for processing.

[0011] Another object of the present invention is to providemelt-processible PTFE that in its unoriented solid form has acrystallinity of between about 1% and about 60% and good mechanicalproperties.

[0012] Still another object of the present invention is to provide amelt-blending method that yields melt-processible, thermoplastic PTFEcompositions of good mechanical properties comprising PTFE grades thatare characterized in having a non-zero melt-flow index in a particularrange.

[0013] Additionally, it is an object of the present invention to providea method to melt-process PTFE compositions that comprise PTFE gradesthat are characterized in having a non-zero melt-flow index in aparticular range, into useful shapes and articles of good mechanicalproperties.

[0014] Still another object of the present invention is to provideuseful shapes and articles of good mechanical properties that aremanufactured by melt-processing of PTFE compositions that comprise PTFEgrades that are characterized in having a non-zero melt-flow index in aparticular range.

[0015] Yet another object of this invention is to provide novel usefulshapes and articles that comprise PTFE.

[0016] Additional objects, advantages and novel features of the presentinvention will be set forth in part in the description which follows,and in part will become apparent to those skilled in the art onexamination of the following, or may be learned by practice of theinvention. The objects and advantages of the invention may be realizedand attained by means of the instrumentalities and combinationsparticularly pointed out in the appended claims.

[0017] The present invention provides a melt-processible fluoropolymerhaving a peak melting temperature of at least 320° C. and goodmechanical properties. And compositions and articles comprising at leastin part a continuous polymeric phase comprising a melt-processiblefluoropolymer having a peak melting temperature of at least 320° C. andgood mechanical properties.

[0018] The present invention also provides a composition comprising amelt-processible tetrafluoroethylene polymer, or a melt-processibleblend of two or more tetrafluoroethylene polymers wherein said polymeror said blend of two or more polymers has good mechanical properties.And a process for producing a melt-processible composition comprising amelt-processible tetrafluoroethylene polymer, or a melt-processibleblend of two or more tetrafluoroethylene polymers wherein said polymeror said blend of two or more polymers has good mechanical properties.Also a method for producing an article comprising melt-processing acomposition comprising a melt-processible tetrafluoroethylene polymer,or a melt-processible blend of two or more tetrafluoroethylene polymerswherein said polymer or said blend of two or more polymers has goodmechanical properties.

[0019] Another aspect of the present inventions includes using themelt-processible polymer or polymer composition as an adhesive. Thepresent invention provides a process for connecting parts comprisingadhering a part to at least one further part with the polymer orcomposition of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a stress-strain curve of a melt-processed film of PTFEaccording to the present invention.

[0021]FIG. 2 is a prior art commercial, sintered and skived film ofstandard (ultra-high molecular weight) PTFE.

DETAILED DESCRIPTION OF THE INVENTION

[0022] The following is a list of defined terms used herein:

[0023] Void free-refers to a polymer or polymer composition, below itscrystallization temperature, having a void content lower than sinteredtetrafluoroethylene polymers including sintered tetrafluoroethylenepolymers modified up to 0.1 wt % with PPVE (which are reported to have avoid content of 2.6% or higher in the Modern Fluoropolymers, J. Scheirs,Ed. Wiley (New York 1997) at p. 253). Preferably, void free refers to apolymer or polymer composition, below its crystallization temperature,having a void content lower than 2% as determined by measuringgravimetrically the (apparent) density of a specimen and the intrinsicdensity via its IR spectroscopically determined amorphous content (asdiscussed in the Modern Fluoropolymers, J. Scheirs, Ed. Wiley (New York1997) at pp. 240-255, in particular p. 253; the entire disclosure ofwhich is, 1997, p. 240).

[0024] Monomeric units—refers to a portion of a polymer that correspondsto the monomer reactant used to form the polymer. For example, —CF₂CF₂—represents a monomeric unit derived from the monomer reactanttetrafluoroethylene.

[0025] The poly(tetrafluoroethylene)s

[0026] The PTFE's according to the present invention generally arepolymers of tetrafluoroethylene. Within the scope of the presentinvention it is contemplated, however, that the PTFE may also compriseminor amounts of one or more co-monomers such as hexafluoropropylene,perfluoro(methyl vinyl ether), perfluoro(propyl vinyl ether),perfluoro-(2,2-dimethyl-1,3-dioxole), and the like, provided, howeverthat the latter do not significantly adversely affect the uniqueproperties, such as thermal and chemical stability of the PTFEhomopolymer. Preferably, the amount of such co-monomer does not exceedabout 3 mole percent (herein “mol %’), and more preferably less thanabout 1 mol %, particularly preferred is a co-monomer content of lessthan 0.5 mol %. In the case that the overall co-monomer content isgreater than 0.5 mol %, it is preferred that amount of the aperfluoro(alkyl vinylether) co-monomer is less than about 0.5 mol %; andmore preferably less than about 0.2 mol %. Suitable polymers includethose having a peak melting temperature, as measured under standardconditions, that exceeds about 320° C., preferably above 325° C. andmore particularly above 327° C. Preferably the polymer will have no peakmelting temperatures below 320° C. and more preferably the polymer willhave a single peak melting point which is above 320° C. Most preferredare PTFE homopolymers.

[0027] In addition, suitable poly(tetrafluoroethylene)s according to thepresent invention include those having good mechanical properties, suchas, for example, a highly beneficial thermoplastic flow behavior. Anindication of the thermoplastic flow behavior of the polymer can bereadily analyzed with the commonly employed method of the determinationof a melt-flow index (MFI). The latter method, for the present PTFE's isconveniently and reproducibly carried out according to ASTM testD1238-88, at 380° C. under a load of 21.6 kg, herein referred to as themelt flow index or alternatively MFI (380/21.6). Under theseexperimental conditions, and in a maximum extrudate-collection time of 1hr, conventional ultra-high molecular weight PTFE grades have an MFI ofzero.

[0028] Preferably, the PTFE grades according to the present inventionhave a non-zero MFI (380/21.6) of less than about 2.5 g/10 min in amaximum extrudate-collection time of 1 hr. More preferably, the PTFE'sare characterized by an MFI (380/21.6) between about 0.0005 and about2.5 g/10 min, more preferably between about 0.2 g/10 min and about 2.5g/10 min and most preferably between 0.25 g/10 min and about 2.5 g/10min. Although the choice of the PTFE grades used will to some extentdepend on the particular end product, an MFI range of about 0.25 toabout 2 g/10 min is preferred for most applications. In the case thatthe PTFE grades according to the present invention comprise a relativelyhigh content of comonomer the upper limit of the MFI range of thepreferred grades could be higher. For example, if the PTFE contains upto 3 mol % of comonomer, the upper limit of the MFI range could extendup to about 25 g/10 min, and a preferred range would be between 0.1 upto about 15; when the comonomer content is about 1 mol % or less, theMFI range may extend up to about 15 g/10 min, more preferably the MFIrange would be between 0.1 up to about 10; and at a content of 0.3 mol %or less the suitable MFI would next exceed about 5 g/10 min and morepreferably would have an MFI value in the above-noted range for PTFEpolymers.

[0029] The highly beneficial thermoplastic flow behavior of thepoly(tetrafluoroethylene)s according to the present invention ischaracterized by their linear visco-elastic behavior, which isconveniently expressed as the absolute value of the complex viscosity.Preferably, the PTFE grades according to the present invention have aplateau value of the complex viscosity measured at frequencies belowabout 0.01 rad/s and at a temperature of 380° C. of between about 4.10⁵and about 10⁹ Pa.s; preferably between about 7.10⁵ and about 10⁸ morepreferably at least 1.5×10⁷ Pa.s; and most preferred between about 10⁶and about 5.10⁷ Pa.s.

[0030] The poly(tetrafluoroethylene)s according to the present inventionin addition to having good mechanical properties, are characterized in arelatively low crystallinity which is beneficial for the toughness ofproducts fabricated thereof. This degree of crystallinity isconveniently determined by differential scanning calorimetry (DSC)according to standard methods known to those skilled in the art ofpolymer analysis. Preferably, once-molten PTFE grades according to thepresent invention that are recrystallized by cooling under ambientpressure at a cooling rate of 10° C./min in unoriented form have adegree of crystallinity of between about 1% about 60%, preferablybetween about 5% and about 60%, more preferably at least about 45% andnot more than 55% based on a value of 102.1 J/g for 100% crystallinePTFE (Starkweather, H. W., Jr. et al., J. Polym. Sci., Polym. Phys. Ed.,Vol. 20, 751 (1982)).

[0031] Preferably, the PTFE grades according to the present inventionare characterized by an MFI (380/21.6) between about 0.25 to about 2g/10 min and a degree of crystallinity of once-molten and recrystallizedunoriented material of between about 5%, preferably above 45% and lessthen about 60%, preferably less than 55%. More preferably, the PTFEpolymer is a polymer having a single peak melting point temperaturewhich is above 325° C. and is preferably a homogenous blend of polymersand/or homopolymer.

[0032] The PTFE grades of the present invention can be synthesizedaccording to standard chemical methods for the polymerization oftetrafluoroethylene as described in detail in the literature (forexample, W. H. Tuminello et al., Macromolecules, Vol. 21, pp. 2606-2610(1988)) and as practiced in the art. Additionally, PTFE grades accordingto the present invention can be prepared by controlled degradation ofcommon, high molecular weight PTFE, for example by controlled thermaldecomposition, electron beam, gamma- or other radiation, and the like(Modern Fluoropolymers, J. Scheirs, Ed. Wiley (New York), 1997 theentire disclosure of which is hereby incorporated by reference).Furthermore, and as demonstrated in the present invention, the PTFEgrades according to the present invention can be manufactured byblending of, for example, high melt-flow index grades with appropriateamounts of grades of a lower, for instance below 0.5 g/10 min, or evenzero melt-flow index to yield mixed materials with values of themelt-flow index, viscosity or crystallinity in the desired range. Due tothe relatively simple nature of the MFI-testing method, viscositymeasurement and crystallinity determination, using, for example, theseanalytical tools, those skilled in the art of polymer blending canreadily adjust the relative portions of the different PTFE grades toobtain the melt-processible, thermoplastic PTFE compositions accordingto the present invention.

[0033] The present invention also contemplates compositions and articlescomprising a continuous phase having at least 15 wt. %, preferably atleast 45 wt. %, and more preferably at least 95 wt. % of themelt-processible tetrafluoroethylene polymer including polymers that areformed by blending two or more tetrafluoroethylene polymers of thepresent invention. An exemplary composition could include a compositionor an article wherein the continuous phase composed of at least 99 wt. %of a PTFE homopolymer filled with a filler such as talc, glass and/orother inorganic or organic particles. It may be that the filler comprisea between 10 to 90 wt. %, preferably between 10 and 45 wt % and morepreferably less than 30 wt. % of the total composition (includingcontinuous phase and filler).

[0034] The compositions according to the present invention optionallymay include other polymers, additives, agents, colorants, fillers (e.g.,reinforcement and/or for cost-reduction), property-enhancement purposesand the like, reinforcing matter, such as glass-, aramid-, carbon fibersand the like, plasticizers, lubricants, processing aids, blowing orfoaming agents, electrically conducting matter, other polymers,including poly(tetrafluoroethylene), fluorinated polymers andcopolymers, polyolefin polymers and copolymers, and rubbes andthermoplastic rubber blends, and the like. Depending on the particularapplication, one or more of the above optional additional ingredientsand their respective amounts are selected according to standardpractices known to those skilled in the art of standard polymerprocessing, compounding and applications.

[0035] Processing

[0036] The PTFE compositions according to the present invention can beprocessed into useful materials, neat or compounded, single- andmulti-component shapes and articles using common melt-processing methodsused for thermoplastic polymers that are well known in the art. Typicalexamples of such methods are granulation, pelletizing, (melt-)compounding, melt-blending, injection molding, melt-blowing,melt-compression molding, melt-extrusion, melt-casting, melt-spinning,blow molding, melt-coating, melt-adhesion, welding, melt-rotationmolding, dip-blow-molding, melt-impregnation, extrusion blow-molding,melt-roll coating, embossing, vacuum forming, melt-coextrusion, foaming,calendering, rolling, and the like.

[0037] Melt-processing of the PTFE compositions according to the presentinvention, in its most general form, comprises heating the compositionto above the crystalline melting temperature of the PTFE's, which, ofonce-molten material, typically are in the range from about 320° C. toabout 335° C. (preferably less than 400° C.), although somewhat lower,and higher temperatures may occur, to yield a viscous polymer fluidphase. Unlike standard (ultra-high molecular weight) PTFE above itscrystalline melting temperature, the PTFE grades according to thepresent invention form homogenous melts that can be freed from voids andmemory of the initial polymer particle morphology. The latter melt isshaped through common means into the desired form, and, subsequently orsimultaneously, cooled to a temperature below the crystalline meltingtemperature of the PTFE's, yielding an object or article of good anduseful mechanical properties. In one preferred embodiment, shaped PTFEmelts are rapidly quenched at a cooling rate of more than 10° C./min,more preferably more than 50° C./min, to below the crystallizationtemperature to yield objects, such as fibers and films, of highertoughness.

[0038] Certain articles, such as, but not limited to, fibers and filmsmade according to the present invention optionally may, subsequently, bedrawn or otherwise deformed in one or more directions, embossed, and thelike to further improve the physico-chemical, mechanical, barrier,optical and/or surface properties, or be otherwise post-treated (forinstance, quenched, heat treated, pressure treated, and/or chemicallytreated). The above methods and numerous modifications thereof and otherforming and shaping, and post-processing techniques are well know andcommonly practiced. Those skilled in the art of processing ofthermoplastic polymers are capable of selecting the appropriatemelt-processing and optional post-processing technology that is mosteconomical and appropriate for the desired end product, or productintermediate.

[0039] Products and Applications

[0040] The products contemplated according to the present invention arenumerous, and cover vastly different fields of applications. This isespecially true as PTFE has been approved for food contact and forbiomedical applications. Without limiting the scope and use of thepresent invention, some illustrative products are indicated hereafter.Generally speaking, the products and materials according to the presentinvention include most or all applications that currently are covered bystandard (ultra-high molecular weight) PTFE, and many of its modified,melt-processible co-polymers. In many cases, the present products, whencompared with the latter, will have superior physical-chemicalproperties due to their predominant homopolymer character. Thus,applications are envisioned, among other industries, in the wire andcable industry, the printed-circuit board industry, the chemicalprocessing industry, the semiconductor industry, the automotiveindustry, out-door products and coatings industry, the food industry,the biomedical industry, and more generally in industries and uses whereany combination of high release, anti-stick, high-temperature stability,high chemical resistance, flame-resistance, anti-fouling, UV resistance,low friction, and low dielectric constant is required.

[0041] In particular, the PTFE may be used to form at least parts inarticles such as, for example, is a wire (and/or wire coating), anoptical fiber (and/or coating), a cable, a printed-circuit board, asemiconductor, an automotive part, an outdoor product, a food, abiomedical intermediate or product, a composite material, a melt-spunmono-or multi-filament fiber, an oriented or un-oriented fiber, ahollow, porous or dense component; a woven or non-woven fabric, afilter, a membrane, a film, a multi-layer-and/or multicomponent film, abarrier film, a container, a bag, a bottle, a rod, a liner, a vessel, apipe, a pump, a valve, an O-ring, an expansion joint, a gasket, a heatexchanger, an injection-molded article, a see-through article, asealable packaging, a profile, and/or a thermoplastically welded part.Preferred articles may include fibers, films, coatings and articlescomprising the same.

[0042] Typical examples of intermediate and end-user products that canbe made according to the present invention include, but are not limitedto granulate, thermoplastic composites, melt-spun mono- andmulti-filament fibers, oriented and not, hollow, porous and dense,single- and multi-component; fabrics, non-wovens, cloths, felts,filters, gas house filtration bags; sheets, membranes, films (thin andthick, dense and porous); containers, bags, bottles, generally simpleand complex parts, rods, tubes, profiles, linings and internalcomponents for vessels, tanks, columns, pipes, fittings, pumps andvalves; O-rings, seals, gaskets, heat exchangers, hoses, expansionjoints, shrinkable tubes; coatings, such as protective coatings,electrostatic coatings, cable and wire coatings, optical fiber coatings,and the like. The above products and articles may be comprised in partor in total PTFE compositions according to the present invention, oroptionally include dissimilar materials, such as for example inmulti-layer and multi-component films, coatings, injection moldedarticles, containers, pipes, profiles, and the like.

[0043] Due to the fact that the PTFE grades according to the presentinvention can be readily processed into mechanical coherent, tough,thin, dense and/or translucent objects, novel application areas for PTFEare contemplated that heretofore were not readily or economically, if atall, accessible due to the intractability of standard (ultra-highmolecular weight) grades, notably in areas where the absence of remnantsof powder morphology and voids have prohibited use of the lattermaterial. Preferably, the polymer of the present invention hassufficient clarity such that if it were formed into a 1 mm thick film,and tested at a temperature below its crystallization temperature, itwould be sufficiently translucent to enable images viewed through thefilm to be readily recognized, preferably without distortion.

[0044] Exemplary applications of the polymer and polymer composition ofthe present which take advantage of some of these beneficial propertiesinclude see-through, sealable packaging, barrier films and caps,conformal coatings, dense tubing and linings, thin-walled and complexinjection-molded parts, and the like.

[0045] The PTFE grades according to the present invention, due to theirthermoplastic nature, not only are useful for the simple and economicproduction of finished goods and intermediate products, but also forother functions. An illustrative example of such function, withoutlimiting the scope of the present invention, is adhesion and welding.The latter is a well-recognized difficulty associated with common PTFE(Modern Fluoropolymers, J. Scheirs, Ed. Wiley (New York), 1997, p. 251).The PTFE grades according to the present invention were found to beoutstanding adhesives, for example, for itself as well as for otherfluoropolymers, preferably including common high-molecular weight PTFEproducts such as films, sheets and the like. Simply by inserting a smallamount of a PTFE grade according to the present invention in powder,film or other form between two or more surfaces that one desires toadhere together, liquefying the former material, and subsequentlysolidifying under slight or modest pressure, it was found to yield avery strong adhesive bond that was provided by the inventive PTFEgrades.

[0046] The following specific examples are presented to illustratevarious aspects of the present invention and are not to be construed aslimitations thereon.

EXAMPLES

[0047] The following examples are given as particular embodiments of theinvention and to demonstrate the practice and advantages thereof. It isunderstood that the examples are given by way of illustration and arenot intended to limit the specification or the claims that follow in anymanner.

[0048] General Methods and Materials

[0049] Melt-Flow Index. Values of the melt flow index (MFI) as discussedherein are determined in accordance with the ASTM Standard D1238-88 at atemperature of 380° C. and under a load of 216 kg during a maximumextrudate-collection time of 1 hr using a Zwick 4106 instrument.

[0050] Viscosity. The absolute values of the complex viscosities ofdifferent PTFE grades were measured from small amplitude oscillatoryshear experiments (Rheometrics Dynamic Spectrometer RDS-II) at 380° C.for several frequencies between 100 rad/s and 3.10⁻³ rad/s usingstandard plate-plate geometry. The linear range was estimated fromstrain-sweep experiments at 100 rad/s.

[0051] Thermal Analysis. Thermal analysis was conducted with a Netzschdifferential scanning calorimeter (DSC, model 200). Samples of about 5mg were heated at a standard rate of 10° C./min. Melting temperaturesgiven hereafter refer to the endotherm peak temperatures of once molten(at 380° C.) and cooled (at 10° C./min) material. Crystallinities weredetermined from the enthalpies of fusion of the same specimen taking thevalue of 102.1 J/g for 100% crystalline PTFE (Starkweather, H. W., Jr.et al., J. Polym. Sci., Polym. Phys. Ed., Vol. 20, 751 (1982)).

[0052] Mechanical Data. Tensile tests were carried out with an InstronTensile Tester (model 4411) at room temperature on dumbbell-shapedspecimen of 12 mm gauge length and 2 mm width and fibers. The gaugefiber length was 20 mm. The standard rate of elongation was 100%/min.

[0053] Materials. Various grades of PTFE, purchased from Du Pont(Teflon®, Zonyl®), Ausimont (Algoflon®) and Dyneon, were used. Thefollowing Table I presents an overview of the melting temperatures andthe crystallinities of materials that were once molten at 380° C. andrecrystallized by cooling at 10° C./min, and MFI (380/21.6) of thedifferent grades, which include grades both outside the invention, andthose according to the present invention. TABLE I Melting Crystal- MFIPTFE Temperature* linity (380/21.6) grade (° C.) (%) (g/10 min) IZonyl ® 1200 325.9 64.8 >>1,000 II Zonyl ® 1100 325.0 67.2 >1,000 IIIZonyl ® 1600 329.0 68.9 150 IV Dyneon ® 9207 329.8 65.1 55 V Zonyl ®1000 329.3 59.5 52 VI blend ® V/XX** 331.6 60.5 35 VII Dyneon ® 9201330.5 60.9 22 VIII blend ® V/XX** 331.4 59.9 15 IX Zonyl ® 1300 329.960.5 10 X Algoflon ® F5A EX 330.7 61.7 9 XI Zonyl ® 1400 330.8 57.3 2.8XII Algoflon ® L206 332.3 60.8 2.6 XIII blend ® IX/XX** 331.2 51.9 1.8XIV blend ® XI/XIX** 329.3 49.9 1.2 XV blend ® V/XIX** 329.4 51.4 1.0XVI blend ® XI/XIX** 329.7 47.6 0.8 XVII blend ® IX/XX** 330.5 50.9 0.8XVIII blend ® IX/XX** 331.5 47.5 0.6 XIX Zonyl ® 1500 327.5 44.2 0.2 XXTeflon ® 6 328.6 33.7 0

Comparative Example A

[0054] PTFE grades I-XII (Table I) were melt-compression molded at 380°C. with a Carver press (model M, 25 T) for 5 min at 1 metric ton (t), 10min at 10 t, and then cooled to room temperature during 4 min under 4 tinto plaques of about 4×4×0.1 cm. All grades were found to yield brittleproducts most of which could not be removed from the mold withoutfracture. This example shows that neat grades of PTFE of MFI values morethan about 2.5 cannot be employed to melt-process articles of usefulmechanical properties.

Example 1

[0055] Example A was repeated with PTFE grades XIII-XVIII. The materialswere melt-compression molded at 380° C. with a Carver press (model M, 25T) for 5 min at 1 metric ton (t), 10 min at 10 t, and then cooled toroom temperature during 4 min under 4 t into plaques of about 4×4×0.1cm. These grades were found to yield mechanically coherent, andtranslucent samples that could readily be removed from the mold and bendwithout fracture. This example shows that grades of a non-zero MFIvalue, but less then about 2.5 can be employed to melt-process articlesof PTFE of useful mechanical properties.

Comparative Example B

[0056] Attempts were made to melt-compression mold at 380° C. with aCarver press (model M, 25 T) films of PTFE grades I-XII. All grades werefound to yield brittle products that could not be mechanically removedfrom the mold without fracture. This example shows that neat grades ofMFI values more then about 2.5 cannot be employed to producemelt-processed, free-standing films of useful mechanical properties.

Example 2

[0057] Example B was repeated with PTFE grades XIII-XVIII. The materialswere melt-compression molded at 380° C. with a Carver press (model M, 25T) for 5 min at 1 metric ton (t), 10 min at 10 t, and then cooled toroom temperature during 4 min under 4 t into thin films of about15×15×about 0.025 cm. These grades were found to yield mechanicallycoherent, translucent and flexible films that could readily be removedfrom the mold. This example shows that grades of a non-zero MFI value,but less then about 2.5 can be employed to melt-process thin,mechanically coherent films of PTFE.

[0058] The mechanical properties of the melt-processed PTFE films weremeasured according to the standard method detailed above. A typicalstress-strain curve is presented in FIG. 1(A), for comparison purposes,together with that of a sample of commercial, pre-formed/sintered andskived film of 0.40 mm thickness (B). This figure shows that themelt-processed PTFE film (here of grade XVI (Table I)) has the typicaldeformation properties of a thermoplastic, semi-crystalline polymer witha distinct yield point and strain hardening. The stress-strain curves Aand B resemble each other, which indicates that these melt-processedPTFE films do not have substantially inferior mechanical properties whencompared to common, PTFE of ultra-high molecular weight. The mechanicaldata of the two products are collected in Table II. TABLE II YieldStress Tensile Strength Elongation at PTFE film (MPa) (Nominal, MPa)Break (%) Skived Film 12.8 36.1 476 Melt-processed Film of 12.6 20.9 427PTFE grade XVI

[0059] The excellent mechanical properties of the film according to thepresent invention were not affected by storing the sample for periods inexcess of 15 hrs at temperatures of 200° C. and higher.

[0060] In addition, we observed that the melt-processed PTFE films,unlike the commercial skived material, were dense and translucent,through which text readily could be read up to a film thickness of about1 mm.

Comparative Example C

[0061] PTTE grades I-XII and XX were introduced into a laboratorymelt-spinning apparatus (SpinLine, DACA Instruments), the temperature ofwhich was kept at 380° C., and that was equipped with a die of 1 mmdiameter (length/diameter ratio 1). PTFE grades I-XII could not becollected as monofilaments due to brittleness of the extrudate, leadingto premature fracture. Ultra-high molecular weight PTFE grade XX couldnot be melt-spun, even at loads up to 5 kN (limit of equipment), due tothe high viscosity (zero MFI) of the material.

Example 3

[0062] Example C was repeated with PTFE grade XV. PTFE monofilamentswere collected onto bobbins. The filaments were tough, and could readilybe drawn at room temperature to draw ratios exceeding 4.

[0063] The mechanical properties of the melt-spun fibers were measuredaccording to the method detailed above. Their tensile strength exceeded0.1 GPa.

Comparative Example D

[0064] PTFE grades I-XII and XX were introduced into a laboratory,recycling twin-screw extruder (MicroCompounder, DACA Instruments), thetemperature of which was kept at 380° C., and that was equipped with anexit die of 2 mm diameter. PTFE grades I-XII could not be collected ascontinuous extrudates due to extreme brittleness of the extrudate,leading to premature fracture. Ultra-high molecular weight PTFE grade XXcould not be extruded due to the high viscosity (zero MFI) of thematerial.

Example 4

[0065] Example D was repeated with PTFE grades XIII-XVIII. ContinuousPTFE extrudates were readily collected. The extrudates could readily bechopped into granulate or drawn into monofilaments.

Example 5

[0066] PTFE grade XV was melt-compounded at 380° C. in a Brabender DSK25segmented, co-rotating extruder (25 mm diameter; 22 aspect ratio) with0.1 weight % of various dyes (Amaplast® Blue HB, Red RP, Yellow NX,ColorChem Int. Corp.), 10% of TiO₂ (Fluka), 10 weight % of aramid pulp(Twaron®, Akzo Nobel), and 20 weight % of chopped, 15 mm long carbonfiber, respectively. Subsequently, the compounded materials obtainedwere melt-processed into plaques according to the method in Example 1.Optical microscopy on thin sections (about 0.1 mm) revealed that in allcases extremely homogeneous mixtures and composites were obtained. Thisexample shows that PTFE according to the present invention can bemelt-compounded.

Comparative Example E

[0067] Two strips of about 7×1×0.04 cm of commercial, skived film ofhigh molecular weight PTFE were pressed together in a Carver press(model M, 25T) at a temperature of 380° C. under a load of less than 1 tfor 2 min and subsequently cooled to room temperature. Without muchforce, the strips could be separated from each other, which isindicative of poor adhesion, and illustrates the difficultiesencountered in welding of common PTFE.

Example 6

[0068] Example E was repeated. However, a small piece of melt-processedfilm of PTFE grade XV (about 1×1×0.02 cm) was placed in between the twostrips of about 7×1×0.04 cm of commercial, skived film of high molecularweight PTFE. This sandwich structure was also pressed together in aCarver press (model M, 25T) at a temperature of 380° C. under a load ofless than 1 t for 2 min and, subsequently, cooled to room temperature.The strips could be separated from each other only after one or both ofthe skived material strips exhibited excessive plastic deformation,which is indicative of outstanding adhesive properties of this grade to,for example, common PTFE.

Example 7

[0069] Various amounts (total quantity 90 g) of PTFE grades V and XIX,XI and XIX, and IX and XX, respectively, (see Table I) were introducedinto a Brabender melt-kneader (model Plasti-corder PL 2000), which waskept at a temperature of about. 380° C., 60 rpm. After about 1 min, aclear homogeneous melt was formed that behaved like a melt of ordinarythermoplastics. Mixing was continued for 10 min, after which the blendedproduct was discharged. The MFI values of the different blends weremeasured. The results are given in Table III. TABLE III Weight Ratio MFI(380/21.6) PTFE grades (-) (g/10 min) IX + XX 45-55 0.6 IX + XX 50-500.8 XI + XIX 10-90 0.8 V + XIIX 12.5-87.5 1.0 XI + XIX 25-75 1.2 IX + XX60-40 1.8

[0070] This example shows that PTFE grades according to the presentinvention of an MFI value in the desired range can be prepared bymelt-blending of PTFE grades of which one or more are of too high or/andtoo low values of their respective MFI.

Example 8

[0071] Various amounts (total quantity 90 g) of PTFE grades V and XIX,and IX and XX, respectively, (see Table 1) were introduced into aBrabender melt-kneader (model Plasti-corder PL 2000), which was kept ata temperature of about 380° C., 60 rpm. After about 1 min, a clearhomogeneous melt was formed that behaved like a melt of ordinarythermoplastics. Mixing was continued for 10 min, after which the blendedproduct was discharged. The absolute values of the complex viscositiesof various PTFE samples were measured from small amplitude oscillatoryshear experiments. The results are given in Table IV. TABLE IV WeightRatio Viscosity PTFE grades (-) (Pa.s) V + XIX 60-40 9.3. 10⁵ V + XIX40-60 5.5. 10⁶ V + XIX 20-80 8.4. 10⁶ V + XIX 10-90 1.3. 10⁷ IX + XX60-40 1.2. 10⁷ IX + XX 50-50 1.8. 10⁷ IX + XX 45-55 2.4. 10⁷

[0072] The same PTFE samples were processed into films according to themethod in Example 2. All films were found to exhibit good mechanicalproperties.

[0073] Having described specific embodiments of the present invention,it will be understood that many modifications thereof will readilyappear or may be suggested to those skilled in the art, and it isintended therefore that this invention is limited only by the spirit andscope of the following claims.

What is claimed is:
 1. A melt-processible fluoropolymer having a peakmelting temperature of at least 320° C. and good mechanical properties.2. The fluoropolymer according to claim 1 wherein the fluoropolymer hasan elongation at break of greater than 10%.
 3. The fluoropolymeraccording to any one of claims 1-2 wherein said fluoropolymer has amelt-flow index of greater than 0.2 g/10 min and less than 2.5 g/10 min.4. The fluoropolymer according any one of claims 1-3 wherein saidfluoropolymer is polytetrafluoroethylene.
 5. The fluoropolymer accordingto any one of claims 1-4 wherein the fluoropolymer comprises a minoramount of at least one or more fluoro-monomeric units different from atetrafluoroethylene monomeric unit.
 6. The fluoropolymer according toany one of claims 1-5 wherein said fluoropolymer comprises at least oneor more fluoro-monomeric units derived from hexafluoropropylene,perfluoro(alkyl vinyl ether), and/orperfluoro-(2,2,-dimethyl-1,3-dioxole).
 7. The fluoropolymer according toany one of claims 5-6 wherein the amount of said at least one or morefluoro-monomeric units in said fluoropolymer is less than 3 mol %. 8.The fluoropolymer according to any one of claims 5-6 wherein the amountof fluoro-monomeric units derived from perfluoro(alkyl vinylether) insaid fluoropolymer is less than 0.5 mol %.
 9. The fluoropolymeraccording to any one of claims 1-8 wherein the fluoropolymer, afterbeing once molten, has a crystallinity of between 1% and 60%.
 10. Thefluoropolymer according to any one of claims 1-9 wherein thefluoropolymer has an absolute value of the complex viscosity, measuredat 0.01 rad/s, of between 1.5×10⁷ Pa.s and 10⁹ Pa.s.
 11. Thefluoropolymer according to any one of claims 1-10 wherein thefluoropolymer is void free.
 12. The fluoropolymer according to any oneof claims 1-11 wherein a 1 mm thick film of said fluoropolymer issufficiently clear, at a temperature below its crystallizationtemperature, to enable images viewed through the film to be readilyrecognized.
 13. A composition comprising a continuous polymeric phasecomprising the fluoropolymer according to any one of claims 1-12. 14.The composition according to claim 13 wherein the composition comprisesa continuous phase having at least about 15 wt % of said fluoropolymer.15. An article comprising the fluoropolymer according to any one ofclaims 1-14.
 16. The article of claim 15 wherein the article is formedat least in part by melt processing said fluoropolymer.
 17. The articleaccording to any one of claims 15-16 wherein said article is a wire, anoptical fiber, a cable, a printed-circuit board, a semiconductor, anautomotive part, an outdoor product, a food, a biomedical intermediateor product, a composite material, a melt-spun mono- or multi-filamentfiber, an oriented or un-oriented fiber, a hollow, porous or densecomponent; a woven or non-woven fabric, a filter, a membrane, a film, amulti-layer- and/or multicomponent film, a barrier film, a container, abag, a bottle, a rod, a liner, a vessel, a pipe, a pump, a valve, anO-ring, an expansion joint, a gasket, a heat exchanger, aninjection-molded article, a see-through article, a sealable packaging, aprofile, and/or a thermoplastically welded part.
 18. The articleaccording to any one of claims 15-17 wherein said fluoropolymer adherestwo more parts together wherein at least one of said parts comprisestetrafluoroethylene polymer.
 19. A composition comprising: amelt-processible tetrafluoroethylene polymer, or a melt-processibleblend of two or more tetrafluoroethylene polymers wherein said polymeror said blend of two or more polymers has good mechanical properties.20. The composition according to claim 19 wherein said polymer or saidblend of two or more polymers has a peak melting temperature of at least320° C.
 21. The composition according to any one of claims 19-20 whereinsaid polymer or said blend of two or more polymers has a melt flow indexof greater than 0.2 g/10 min and less than 2.5 g/10 min.
 22. Thecomposition according to any one of claims 19-21 wherein said polymer orsaid blend of two or more polymers has an elongation at break of greaterthan 10%.
 23. The composition according to any one of claims 19-22wherein said polymer or at least one polymer of said blend of two ormore polymers comprises a minor amount of at least one or morefluoro-monomeric units different from a tetrafluoroethylene monomericunit.
 24. The composition according to claim 23 wherein said at leastone or more fluoro-monomeric units is derived from hexafluoropropylene,perfluoro(alkyl vinyl ether), and perfluoro-(2,2,-dimethyl-1,3-dioxole).25. The composition according to any one of claims 23-24 wherein theamount of said at least one or more fluoro-monomeric units in saidpolymer or in said at least one polymer of said blend of two or morepolymers is less than 3 mol %.
 26. The composition according to any oneof claims 23-25 wherein the amount of fluoro-monomeric units derivedfrom perfluoro(alkyl vinylether) in said polymer or in said at least onepolymer of said blend of two or more polymers is less than 0.5 mol %.27. The composition according to any one of claims 19-26 wherein saidpolymer or said blend of two or more polymers, after being once molten,has a crystallinity of between 1% and 60%.
 28. The composition accordingto any one of claims 19-27 wherein said polymer or said blend of two ormore polymers has a melt-flow index of between 0.25 g/10 min and 2 g/10min.
 29. The composition according to any one of claims 19-28 whereinsaid polymer or said blend of two or more polymers has an absolute valueof the complex viscosity, measured at 0.01 rad/s, of between 1.5×10⁷Pa.s and 10⁹ Pa.s.
 30. The composition according to any one of claims19-29 wherein the composition further comprises other polymers, fillers,additives, agents, and/or colorants.
 31. The composition according toany one of claims 19-30 wherein the composition further comprises otherfluorinated polymers and/or copolymers, polyolefin polymers and/orcopolymers, and/or rubbers and/or thermoplastic rubber blends.
 32. Thecomposition according to any one of claims 19-31 wherein the compositionis void free.
 33. The composition according to any one of claims 19-32wherein a 1 mm thick film of the composition is translucent, at atemperature below its crystallization temperature.
 34. A method forproducing a melt-processible composition comprising: forming a polymercomposition according to any one of claims 19-33.
 35. The methodaccording to claim 34 wherein said polymer or at least one of said blendof two or more polymers is formed at least in part by polymerizingtetrafluoroethylene.
 36. The method according to any one of claims 34-35wherein said polymer or at least one of said blend of two or morepolymers is formed at least in part by degrading a tetrafluoroethylenepolymer.
 37. The method according to any one of claims 34-36 whereinsaid polymer or said blend of polymers is formed at least in part byblending two or more tetrafluoroethylene polymers.
 38. The methodaccording to any one of claims 34-37 wherein the polymer composition isformed at least in part by blending one or more polymers or polymermixtures having a melt flow index of less than 0.5 g/10 min.
 39. Themethod according to any one of claims 34-38 wherein the melt-processiblecomposition is formed into an article.
 40. A method for producing anarticle comprising melt-processing a composition comprising: amelt-processible tetrafluoroethylene polymer, or a melt-processibleblend of two or more tetrafluoroethylene polymers wherein said polymeror said blend of two or more polymers has good mechanical properties.41. The method according to claim 40 wherein said polymer or said blendof two or more polymers has an elongation at break of greater than 10%.42. The method according to any one of claims 40-41 wherein said polymercomposition has a melt-flow index of greater than 0 g/10 min and lessthan 25 g/10 min.
 43. The method according to any one of claims 40-42wherein the melt-processible composition has a complex viscosity,measured at 0.01 rad/s, of between 4×10⁹ Pa.s and 10⁹ Pa.s.
 44. Themethod according to any one of claims 40-43 wherein the melt-processiblecomposition, after being once molten, has a crystallinity of between 1%and 60%.
 45. The method according to any one of claims 40-44 whereinmelt-processing includes granulating, pelletizing, melt-compounding,melt-blending, injection molding, melt-blowing, melt-compressionmolding, melt-extruding, melt-casting, melt-spinning, blow-molding,melt-coating, melt-adhering, welding, melt-rotating, molding,dip-blow-molding, melt-impregnating, extrusion blow-molding, melt-rollcoating, embossing, vacuum forming, melt-coextruding, foaming,calendering and/or rolling.
 46. A process for connecting partscomprising: adhering a part to at least one further part with thecomposition according to any one of claims 19-33.
 47. The processaccording to claim 46 wherein at least one of said parts comprises afluoropolymer.
 48. The process according to any one of claims 46-47wherein at least one of said parts comprises tetrafluoroethylenepolymer.